Mystery surrounds bright green substance in water at Sydney beach

Photos were shared on Facebook by worried Cronulla locals.

A mysterious green substance in the water at a Sydney beach on the weekend baffled locals, with many questioning how the fluorescent liquid came to be in the waterways.

Residents from the Sutherland Shire on Friday asked "what is this?" alongside photos of the rock pools at Cronulla, in the city's south, and wondered if the vibrant liquid is cause for alarm.

Photos show a puddle of water over the rocks displaying a tint of fluro green, while another shows the liquid spewing from a tiny pipe onto the rocks.

Green water Cronulla Sydney.
Residents from Cronulla in Sydney's south became concerned after seeing the water had turned green. Source: Facebook

Sydney scenes compared to Venice water stunt

Some compared the sight to the canals in Venice, Italy which were mysteriously dyed green last week. Climate change protestors were thought to be behind the act in Venice but water samples revealed the presence of a non-toxic tinting agent called fluorescein, local media reported. It's likely the case here in Sydney too, the NSW Environment Protection Authority (EPA) suggested, however, there's been no suggestion made that activists are behind the Sydney scenario.

What is the green dye fluorescein?

"Based on the images provided we believe the discolouration is likely to be fluorescein dye, which is commonly used in plumbing/drain testing and dissipates quickly once diluted," an Environment Protection Authority spokesperson told Yahoo. "Fluorescein has low toxicity but even small amounts can be highly visual and for this reason its use should always be minimised."

Grand Canal in Venice turned green by non-toxic chemical in May 2023.
Italian authorities launched an investigation after the canals in Venice turned green last week. Source: AP/Luigi Costantini

Fluorescein is said to be "non-toxic to the environment and is odourless," the product's manufacturer says. But we should still tread with caution, Ian Wright, a water researcher and scientist and associate professor at Western Sydney University, told Yahoo.

He noted the safety data sheet for the product shows it has several human health risks and should be used very carefully. It also warns "do not let this chemical enter the environment," he pointed out.

"Any chemical product should be used very cautiously. Being able to see a visible stain is a cause for concern. But perhaps also it has helped a plumber stop a leak of sewage or other wastewater from a natural waterway," he said.

Green water Cronulla Sydney
The rock pools in Cronulla, Sydney had turned green over the weekend. Source: Facebook

'Doesn't look good'

Some residents commented on the Facebook post suggesting it was fluorescein with one noting it's "legal to use in stormwater drains". Others agreed it was mostly "harmless".

"Doesn’t look good whatever it is," one person hit back. While others swore off swimming until the liquid was gone.

The Sutherland Shire council was made aware of the incident, a spokesperson told Yahoo News on Monday. Sydney Water confirmed it was not their doing. Anyone concerned about possible water pollution should contact the EPA as soon as possible to ensure their concerns can be investigated promptly.

Similar reports have been made in waterways across the country. First in a creek in the Yarra Valley and in Rushcutters Bay Park in Sydney. One woman admitted it looked "very strange" as she shared a video on Facebook.

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